The long-term goal of this proposed project is to understand fundamental neuronal mechanisms underlying higher brain functions that control complex behaviors. Disruption of higher brain functions, such as learning and memory, can occur for a number of reasons including brain surgery, chronic alcohol abuse, head injury, anoxia, and various neurodegenerative disorders such as Alzheimer's disease. A basic understanding of how anatomically distinct neurons in the brain communicate with one another to manipulate complex behavior is essential for the prevention and treatment of many disorders affecting higher brain functions. Recent studies indicate that molecules and cellular mechanisms responsible for important biological processes, including learning and memory, are well conserved among distantly related species. In this project, Drosophila male courtship, which consists of a highly stereotypical sequence of activities and also shows considerable experience-dependent plasticity, will be used as a physiological model of higher-order brain functions. Specific aims of the project are to identify the neuronal subsets involved in the learning/memory process of the courtship plasticity and to determine the temporal requirements of neuronal activity during different phases of the memory formation. To accomplish these aims, a novel molecular genetic approach has been established. In this approach a temperature-sensitive allele of the Drosophila shibire gene (shi") is expressed in restricted neuronal subsets using the GAL4IUAS system. Then, synaptic transmission of the targeted neurons is blocked rapidly and reversibly by a mild temperature-shift in intact animals. By taking advantage of the large collection of available GAL4 lines that are specific to restricted brain regions, the significance of particular neuronal subsets in the courtship plasticity will be determined. A combination of genetic and morphological analysis will be applied to further investigate the neuronal subsets whose functional significance is revealed. The neuronal subsets involved in the genetically determined, stereotypical aspects of male courtship will be also identified using the same approach. The anticipated results, together with the accumulated information of Drosophila behavioral genetics, will provide new insight into the neuronal mechanisms of higher-brain functions in flies, and will contribute to the development of conceptual frameworks for the study of complex behaviors in higher vertebrates including humans.